Electronic apparatus typically include therein electronic modules such as different subsystems, circuits, and so on. These electronic modules usually require different supply voltages (e.g., 1.8 volts, 2.5 volts etc.) for achieving normal operations. To ensure normal operations of every electronic module in electronic apparatus, a voltage converter is typically utilized to convert a DC voltage (e.g., a voltage from a battery) to another different DC voltage as required by every electronic module, that is, a specific input voltage Vin is converted into a different output voltage Vout.
In existing voltage converters, for example, electric energy at an input is stored transitorily in an inductor and/or a capacitor (e.g., a charging process is performed), and thereafter the electric energy is released at a different voltage at an output (e.g., a discharging process is performed), so that the input voltage Vin is converted into the desired output voltage Vout. Accordingly, a drive signal is employed to drive a control device (e.g., a switch) in the voltage converter, by which the charging process and the discharging process are controlled so as to obtain the desired output voltage Vout. That is, a turn-on time Ton during which the switch is ON to charge and a turn-off time Toff during which the switch is OFF to discharge are controlled. The turn-on time Ton corresponds to the pulse width of the drive signal.
In the operation process of the voltage converter, the input voltage Vin usually is not fixed, and may generate jumping change. For example, in electronic apparatus such as a mobile phone, a tablet computer, a digital camera etc., a battery therein has relatively large parasitic resistance. When a module (e.g., a flash drive, a RF module) in the electronic apparatus, which requires very large current, is triggered, it may lead to an instant and significant drop for the output voltage of the battery. Therefore, it's desired that the voltage converter has very good transient response characteristic, so that even if there is an instant drop in the output voltage of the battery (corresponding to the input voltage Vin of the voltage converter), the voltage converter can also provide stable output voltage, allowing the electronic modules driven by the voltage converter to operate normally. The transient response characteristic of the voltage converter is closely related to its bandwidth. The larger the bandwidth is, the better the transient response characteristic is; the smaller the bandwidth is, the worse the transient response characteristic is. Therefore, in order to enhance the transient response characteristic of the voltage converter, it is desirable to increase its bandwidth as much as possible. However, when the bandwidth has been increased to a certain extent, the parasitic zero pole at high frequency may be included within the bandwidth, which may make a design of the frequency compensation become very complex and difficult. In addition, as for a boost converter, there is a right-half-plane zero point at low frequency (about several hundred kHz), whose bandwidth has to be set within the right-half-plane zero point to meet the stability requirement, so it is hard to improve the transient response of the boost converter. Hence, the application provides an input voltage feedforward device, which may notably enhance the transient response characteristic of the voltage converter as for a certain bandwidth.